1. Field of the Invention
The present invention relates to an improvement of a piezoelectric vibrating reed, and a piezoelectric device which has received the piezoelectric vibrating reed within a package or a case.
2. Description of the Related Art
A piezoelectric device such as a piezoelectric vibrator or a piezoelectric oscillator is widely employed in a small-sized information apparatus such as an integrated card (IC) card, a hard disk drive (HDD), a mobile computer, a communication apparatus such as a cellular phone, a car phone, a paging system, or a piezoelectric gyro sensor.
FIG. 9 is a schematic plan view of an example of the piezoelectric vibrating reed which has been employed for the piezoelectric device in the related art.
Referring to FIG. 9, an outer shape of the piezoelectric vibrating reed 1 is formed by etching a piezoelectric material such as quartz, and the piezoelectric vibrating reed 1 has a rectangular base 2 to be mounted on a package (not shown), and a pair of vibrating arms 3 and 4 which extend upward from the base 2, and long grooves 3a and 4a are formed in both surfaces of the vibrating reeds, thereby forming a required driver electrode (see JPA 2002-261575).
In such a piezoelectric vibrating reed 1, when the driver electrode is made to apply a drive voltage, leading ends of the vibrating arms 3 and 4 wind and vibrate by being close to and spaced apart from each other, so that signals having predetermined frequencies are taken out.
However, the piezoelectric vibrating reed 1 has extraction electrodes at a location denoted as reference numerals 5 and 6 of the base 2, which is applied with adhesives 7 and 8 to be fixed to a body such as a package.
After the fixation by means of the adhesives, cut portions 9 and 9 are formed in the base 2 so as to prevent a residual stress due to a difference between coefficients of linear expansion between the material for forming constituting the piezoelectric vibrating reed and the material for forming the package or the like from disturbing the winding vibration of the vibrating arms.
As such, a progress in miniaturization has been made in the piezoelectric vibrating reed 1 so that arm widths W1 of the vibrating arms 3 and 4 are about 100 μm, a distance therebetween is about 100 μm, and a width BW1 of the base 2 is about 500 μm. These values are made to decrease, a length BL1 of the base correspondingly decreases, so that the piezoelectric vibrating reed 1 is small-sized.
However, the piezoelectric vibrating reed 1 which has been small-sized has problems in terms of temperature characteristics as follows.
FIG. 10 is a graph illustrating the temperature characteristic of the piezoelectric vibrating reed 1, which particularly illustrates temperature-Crystal Impedance (CI) value characteristics.
As shown in FIG. 10, the temperature-CI value characters are severely unstable in the piezoelectric vibrating reed 1 of the related art.
It is expected that the degradation of the temperature-CI value characteristics is resulted from the change in stress of the location where the base 2 is bonded with the adhesives 7 and 9 due to the change in temperature, and it is also expected that the same effect occurs even when the stress changes in the location where the base 2 is bonded with the adhesives 7 and 9 when a drop impact occurs on the piezoelectric vibrating reed 1.
In particular, when the cut portions 9 and 9 are more cut toward their central directions in order to effectively suppress the CI value by reducing the leakage into the base 2 due to the winding vibration of the vibrating arms, the rigidity of the base 2 is significantly reduced to cause the vibration state to be unstable.